A study to determine if a defect in liver glycogen storage may be present in patients with diabetes mellitus, and if that defect is reversed after a three day fast. In contrast to non-diabetic individuals, glycogen stores increase in patients with type 2 diabetes during a three day fast, and that glucose derived from gluconeogenesis (formation of glucose within the animal body, especially by the liver, from substances other than carbohydrates) is diverted from glucose release into glycogen storage during the fast. The study subject will be admitted to the Clinical Research Center/MCV Hospitals. Water and ice will be consumed after dinner, until the completion of the tests the following morning. If the subject has diabetes mellitus, medication to lower the blood sugar will be temporarily discontinued. Percentage of body fat will be determined by placing EKG (electrocardiogram) electrodes on the hands and feet of the subject, and by measuring the thickness of skinfolds. Two baseline blood samples will be obtained through intravenous catheters. The subject will then be given a sugar solution to drink and further blood samples will be taken every 30 minutes for two hours. The patient will then begin a three day fast, eating or drinking water or ice. On the first night, heavy water (^2H^2O), a naturally occuring varient of water, which is non-radioactive, will be consumed. At 5:00a.m., two small catheters will be placed into arm veins, one to infuse non-radioactive tracers to determine the amount of glucose produced by the liver, the other, to draw blood samples. A loosely-fitting plastic tent will be placed over the head of the quietly resting patient for twenty minutes. This will measure the amount of oxygen intake and carbondioxide output (calorimetry). A urine sample will be obtained to determine the amount of protein used by the body for energy. After the blood samples are obtained on the first day, fasting will continue, along with consumption of water which contains small amounts of heavy water. The same studies that were done on the first day will be repeated on the third day. An injection of glucagon will be given and four additional blood samples will be obtained.